Pro Drupal Development, Second Edition

CHAPTER 10The Form API

Drupal features an application programming interface (API) for generating, validating, and processing HTML forms. The form API abstracts forms into a nested array of properties and values. The array is then rendered by the form rendering engine at the appropriate time while a page is being generated. There are several implications of this approach:

• Rather than output HTML, we create an array and let the engine generate the HTML.
• Since we are dealing with a representation of the form as structured data, we can add, delete, reorder, and change forms. This is especially handy when you want to modify a form created by a different module in a clean and unobtrusive way.
• Any form element can be mapped to any theme function. ...